1. Field of Invention
The invention relates to an optical signal device and, in particular, to an optical signal interleaver that can decrease the interval between adjacent channels and thus increase the total transmission capacity under the existing network structure.
2. Related Art
Along with the emergence of new technologies and increasing Internet uses, the communication transmission capacity has been expanding continuously. Network equipment providers have to provide a larger bandwidth for transmitting more and more AV signals. The technologies of WDM (Wavelength Division Multiplexing) and DWDM (Dense WDM) can largely expand the total transmission capacity under the current optical fiber structure.
DWDM systems enable the transmission of optical carrying different signals through the same optical fiber. The multiplexing/de-multiplexing and adding/dropping of wavelengths are often achieved using optical thin film filters. However, the channel width of optical thin film filters are difficult to be lowered and may easily age with time under high powers. Therefore, lowering the interval between channels in a transmission system is a better way to increase the total transmission capacity, as shown in FIG. 1 where 2f becomes f. For existing optical thin film filter systems, the interval between channels is 200 GHz. If one can lower the adjacent chancel interval down to 100 GHz without modifying the existing optical thin film filter network structure, the total transmission capacity can be doubled by doubling the number of channels.
A few solutions had been proposed before. For example, the U.S. Pat. No. 6,169,626 discloses a periodic spectrometer structure composed of an air-layer Fabry-Perot and a spectrometric prism. Its advantage is that there is a good temperature stability when the thermal expansion of the glass for the air-layer Fabry-Perot. On the other hand, it has the drawback of a larger volume and a lot of components.
An object of the invention is to provide an optical signal interleaver, which, under the condition of same wavelength intervals such as ITU (International Telecommunication Union), multiplexes/de-multiplexes an optical signal with interleaving wavelengths (odd ITU wavelengths and even ITU wavelengths) from an optical fiber, thus increasing the total transmission capacity under the current network structure.
In accordance with the disclosed optical signal interleaver, a plurality of birefringent plates are used to form an optical signal interleaving mechanism to separate all the wavelengths in an optical signal into an E-ray and an O-ray. Therefore, the interval can be decreased. At the same time, using the optical signal interleaver comprised of a polarization beam splitter/combiner, a polarization rotator, a polarization beam displacer, and a beam angle deflector, the incident beam output from an optical fiber collimator (the light signal with all wavelengths) can be separated into an O-ray and an E-ray, which then enter two ports of a double optical fiber collimator. Thus, the invention can increase the total transmission capacity under the current network structure.